Recently, as electronic equipment has been reduced in size, small-sized high-frequency capacitors having large capacitance have been demanded. As such capacitors, a solid electrolytic capacitor using a solid electrolyte layer made of a conductive polymer has been proposed, which comprises a positive electrode, a dielectric layer, and the solid electrolyte layer that is formed on the dielectric layer. In the solid electrolytic capacitor, the positive electrode is composed of a sintered body of valve metal such as tantalum, niobium, titanium, and aluminum, and then the dielectric layer is formed by anodizing a surface of the positive electrode. By using a conductive polymer layer as the solid electrolyte layer, equivalent series resistance (ESR) of the solid electrolytic capacitor can be reduced. However, the conductive polymer layer made of organic material may not enough strongly adhere to the dielectric layer made of inorganic material.
In Japanese Patent Unexamined Publication No. H2-74021, it has been proposed that an adhesion between a dielectric layer and a conductive polymer layer can be improved by a surface treatment with a silane coupling agent to the dielectric layer.